cmd: eeprom: Hide eeprom layout versioning behind a Kconfig option

Add a new Kconfig option EEPROM_LAYOUT_VERSIONS, and hide eeprom
layout versionsing code behind it. Only print the relevant help in
'eeprom' command usage if this option is enabled.

Enable this new option for cm_fx6_defconfig and cm_t43_defconfig.
These are the only boards using EEPROM layout versioning.

Signed-off-by: Marek BehĂșn <kabel@kernel.org>
diff --git a/configs/cm_fx6_defconfig b/configs/cm_fx6_defconfig
index a4d5f91..386616c 100644
--- a/configs/cm_fx6_defconfig
+++ b/configs/cm_fx6_defconfig
@@ -46,6 +46,7 @@
 CONFIG_CMD_GREPENV=y
 CONFIG_CMD_EEPROM=y
 CONFIG_CMD_EEPROM_LAYOUT=y
+CONFIG_EEPROM_LAYOUT_VERSIONS=y
 CONFIG_EEPROM_LAYOUT_HELP_STRING="v2, v3"
 CONFIG_SYS_I2C_EEPROM_BUS=2
 CONFIG_SYS_EEPROM_PAGE_WRITE_BITS=4